Purification of zinc solutions



UNITED STATES PATENT OFFICE.

SAMUEL FIELD, OF LONDON, ENGLAND, ASSIGNOR TO THE METALS EXT-RAG- TION CORPORATION LIMITED, OF LONDON, ENGLAND, A. CORPORATION OF Patented June 21, 1921.

GUERNSEY.

PURIFICATION OF ZINC SOLUTIONS.

1,382,494 Specification of Letters Patent.

No Drawing. Application filed December 17, 1920. Serial N 0. 431,482.

T 0 all whom it may concern:

Be it known that I, SAMUEL FIELD, a subject of the King of England, residing at London, England, have invented certain new and .useful Improvementsin the Purification of Zinc Solutions, of which the following is a specification.

' This invention relates to the purification The metal may be employed in granulated form or as powder, or other state of subdivision which is adapted to provide an extended contact surface. For example, 'zinc fume or blue powder may advantageously be used.

Preferably the zinc solution is acidified, and preferably also the process is carried out with application of heat.

The mercury salt may be added in any convenient way. It may beadded as a solution, or the required quantity of the salt itself may be directly dissolved in the zinc solution to be treated, or at a suitable prior stage in the preparation of the latter.

The salts of mercury utilizable include mercuric chlorid and mercuric nitrate, but it will be appreciated that if the zinc s subsequently to be deposited electrolytically the acid radical in the mercury salt must be of such a nature as not toattack the anodes and cause undue disintegration. A suitable salt in this case is mercuric sulfate.

It is clear also that when the purified zinc solution is to be electrolyzed, the metal or alloy used in conjunction with the mercury salt must be one whose presence in solution will not be detrimental to the electrolytic process. For this purpose, therefore, zinc in a finely divided form is partlcularly suit able. alloy is used, a certain quantity of this metal passes into solution, but this is in no way 6 detrimental to the subsequent electro-deposi- When aluminium or an aluminium tion of the zinc. If desired, however, the aluminium may be subsequently removed concurrently with any iron impurity.

Crude zinc sulfate solutions such as the solutions obtained by'the treatment of a zinc ore, previously calcined, if necessary, with sulfuric acid or acid liquor from electrolytic cells, usually contains various foreign constituents, some of which, although present in very small amount, are nevertheless inadmissible if the solution is to be satisfactorily employed for electro-deposition.

These foreign constituents include salts of iron, arsenic, antimony, bismuth, copper, cadmium, nickel, cobalt and other less common metals which not infrequently occur in zinc bearing ores.

The present invention may be conveniently exemplified in its application in one way to the purification of a zinc solution of this kind for'the subsequent electrolytic deposition of the zinc, it being understood that this example is given for purpose of illustration and not by way of limitation.

To 10 tons of such a solution which has been brought to an acidity of 0.1 to 0.2 per cent, (for instance, by incomplete neutralization, or by complete neutralization for any special purpose, such as the removal of silica, and subsequent acidification with acid or acid liquors), 2 lbs. of mercury in the form of sulfate are added, and then about 40 lbs. of zinc powder, and the liquors are gently stirred while ,bein maintained at a temperature of 7O -1OO- As a first result of this treatment, mercury is deposited upon the zinc owder whic so constitutes a vigorous e ectro-chemical couple. The metallic impurities, for example, copper, arsenic, antimony, bismuth, cadmium, nickel, cobalt and the rarer metals are precipitated upon the mercury in the form of a sludge which may be readily separated from the liquors by decantation or filtration. This sludge may be subsequently treated in any. suitable way for recovery of the mercury, for example, by volatilization of the latter. A considerable proportion of the zinc powder passes into solut1on and is therefore ultimately recovered by electrodeposition.

If any iron present be not completely precipitated it may be removed by any suitable method either before or after the treatment just described.

15 into the solution,

Solutions purified by the process herein set forth are particularly suitable for the recovery of zinc by electro-deposition, but as will be readily understood the invention is equally applicable to the preparation of purified zinc solutions for other purposes.

In my prior United States specification,

Ser. No. 306,874, I have described a process for the purification of zinc solutions according to which the solutions were treated by present process amalgamation is actually brought about in the solution undergoing puri cation.

What I claim as my invention and desire to secure by Letters Patent is 1. The herein described process for the purification of a zinc salt solution from foreign metals, which comprises treating Athe solution with a sub-divided metal more electro-positive than the impurities to be removed, in presence of a salt of mercury.

2. The herein described process for the purification of a zinc salt solution from foreign metals, which comprises treating the solution with a sub-divided alloy more electro-positive than the impurities to be removed, in presence of a salt of mercury.

3. The herein described process for the purification of a zinc salt solution from foreign metals, which comprises treating the acidified solution with a sub-divided metal more electro-positive than the impurities to be removed, in presence of a salt of mercury.

4. The herein described process for the purlfication of a zinc salt solution from foreign metals, which comprises treating the acidified and heated solution with a subdivided metal more electro-positive than the impurities to be removed, in presence of a salt of mercury.

5. The herein described process for the purification of a zinc salt solution from foreign metals, which comprises treating the acidified and heated solution with subdivided zinc in presence of a salt of mercury.

6. The herein described process for the purification of a Zinc salt solution from foreign metals, which comprises treating the acidified and heated solution with subdivided zinc in presence of a salt of mercury in the proportion of about 0.01 per cent. of mercury on the weight of'solution treated.

7. The herein described process for the purification of a zinc salt solution from foreign metals, which comprises treating the acidified and heated solution with subdivided zinc, in presence of mercuric sulfate in the proportion of about 0.01 per cent. of mercury on the Weight of solution treated.

8. The herein described process for the purification of a zinc salt solution from foreign metals, which comprises bringing the solution to an acidity of 0.1 to 0.2 per cent, adding mercuric sulfate in the proportion of about 0.01 er cent. of mercury on the weight of solution treated, adding zinc powder and maintaining the solution at a temperature of 70l00 C.

In testimony whereof I affix my signature.

SAMUEL 'FIELD. 

